Abstract
Abstract. Due to proceeding climate change, some regions such as California face rising weather extremes with dry periods becoming warmer and drier, entailing the risk that wildfires and associated air pollution episodes will continue to increase. November 2018 turned into one of the most severe wildfire episodes on record in California, with two particularly destructive wildfires spreading concurrently through the north and the south of the state. Both fires ignited at the wildland–urban interface, causing many civilian fatalities and forcing the total evacuation of several cities and communities. Here we demonstrate that the inherent carbon monoxide (CO) emissions of the wildfires and subsequent transport can be observed from space by analysing radiance measurements of the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite in the shortwave infrared spectral range. From the determined CO distribution we assess the corresponding air quality burden in major Californian cities caused by the fires and discuss the associated uncertainties. As a result of the prevailing wind conditions, the largest CO load during the first days of the fires is found in Sacramento and San Francisco, with city area averages reaching boundary layer concentration anomalies of about 2.5 mg CO m−3. Even the most polluted city scenes likely comply with the national ambient air quality standards (10 mg CO m−3 with 8 h averaging time). This finding based on dense daily recurrent satellite monitoring is consistent with isolated ground-based air quality measurements.
Highlights
As a consequence of climate change, precipitation and temperature extremes in California during the cool season (October–May) are occurring more frequently with dry periods becoming warmer and drier (Swain et al, 2016), which is associated with an increased fire risk
We have performed an analysis of atmospheric carbon monoxide (CO) concentration changes introduced by emissions of fires using measurements in the shortwave infrared spectral range of TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor satellite
The local CO emissions of Californian wildfires and subsequent transport can be clearly observed from space
Summary
As a consequence of climate change, precipitation and temperature extremes in California during the cool season (October–May) are occurring more frequently with dry periods becoming warmer and drier (Swain et al, 2016), which is associated with an increased fire risk. Equal sensitivity to all altitude levels including the boundary layer can be achieved from radiance measurements of reflected solar radiation in the SWIR part of the spectrum. This was first demonstrated by CO retrievals from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument (Burrows et al, 1995; Bovensmann et al, 1999) onboard ENVISAT (Buchwitz et al, 2004; de Laat et al, 2010) in the 2.3 μm spectral range. The recent TROPOMI offers a unique combination of high precision, accuracy, spatiotemporal resolution, boundary layer sensitivity, and global coverage, fostering the monitoring of nearground CO sources (Borsdorff et al, 2018a; Schneising et al, 2019)
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